1. Field of the Invention
This invention relates to methods and devices for reconstructing the ventricle and for sensing infarcted septum and left ventricle wall during percutaneous left ventricle reconstruction, particularly where there is congestive heart failure.
This invention also relates generally to devices for sizing a ventricle and related methods for positioning the device. More particularly, the invention relates to sizing devices for reducing the ventricular volume to improve the heart's pumping action
2. Description of Related Art
Heart failure occurs when the pumping ability of the heart becomes impaired. The term congestive heart failure (CHF) refers to heart failure that is accompanied by congestion of body tissues. Heart failure may be caused by a variety of conditions, including acute myocardial infarction, hypertension, valvular heart disease, or degenerative conditions of the heart muscle known collectively ad cardiomyopathies. Heart failure may exist as either systolic or diastolic (preserved ejection fraction) failure, and right-sided or sided failure. Systolic failure involves a decrease in cardiac contractility and ejection fraction. In systolic heart failure, the ejection fraction declines progressively with increasing degrees of myocardial dysfunction. With a decrease in ejection fraction, there is a resultant increase in diastolic volume, ventricular dilation, ventricular wall tension, and ventricular end-diastolic pressure.
In certain pathological conditions, the ventricles of the heart become ineffective in pumping the blood, causing a back-up of pressure in the vascular system behind the ventricle. The reduced effectiveness of the heart is usually due to an enlargement of the heart. Coronary artery disease causes approximately 60% of congestive heart failure. Acute myocardial infarction (AMI) due to obstruction of a coronary artery is a common initiating event that can lead ultimately to heart failure. A myocardial ischemia may, for example, cause a portion of a myocardium of the heart to lose its ability to contract. Prolonged ischemia can lead to infarction of a portion of the myocardium (heart muscle) wherein the heart muscle dies and become scar tissue. Once this tissue dies, it no longer as a muscle and cannot contribute to the pumping action of the heart. When the heart tissue is no longer pumping effectively, that portion of the myocardium is said to be hypokinetic, meaning that it is less contractile than the uncompromised myocardial tissue. As this situation worsens, the local area of compromised myocardium may in fact bulge out as the heart contracts, further decreasing the hearts ability to move blood forward. When local wall motion moves in this way it is said to be dyskinetic. The dyskinetic portion of the myocardium may stretch and eventually form an aneurysmic bulge.
One problem with a large dilated left ventricle is that there is a significant increase in wall tension and/or stress both during diastolic filling and during systolic contraction. In a normal heart, the adaptation of muscle hypertrophy (thickening) and ventricular dilatation maintain a fairly constant wall tension for systolic contraction. However, in a failing heart, the ongoing dilation is greater than the hypertrophy and the result is a rising wall tension requirement for systolic contraction. This is felt to be an ongoing insult to the muscle myocyte resulting in further muscle damage. In response, the heart tissue remodels to accommodate the chronically increased filling pressures, further increasing the work that the now-compromised myocardium must perform. This vicious cycle of cardiac failure results in the symptoms of congestive heart failure such as shortness of breath on exertion, edema in the periphery, nocturnal dypsnia (a characteristic shortness of breath that occurs at night after going to bed), weight gain, and fatigue, to name a few. The increase in wall stress also occurs during diastolic filling. The stress increase requires a larger amount of oxygen supply, which can result in exhaustion of the myocardium leading to a reduced cardiac output of the heart.
Heart failure (HF), the heart's inability to pump an adequate volume of blood to the tissues, is the only major cardiovascular condition that continues to increase in incidence in the United States. Approximate 5 million patients are currently diagnosed with HF in the United States. The American Heart Association estimates that between 400,000 and 700,000 new HF cases develop each year. This condition is responsible for an estimated 900,000 hospitalizations annually—more than any other medical condition among the elderly. Approximately 6.5 million hospital days each year are attributed to and related to HF and as many as one third of those patients are readmitted for treatment of symptom recurrence within 90 days. Thus, it is not surprising that the cost of providing advanced medical care for the millions of patients suffering from HF is extraordinarily high—now estimated at more than $38 billion annually.
In certain pathological conditions, the ventricles of the heart become ineffective in pumping the blood, causing a back-up of pressure in the vascular system behind the ventricle. The reduced effectiveness of the heart is usually due to an enlargement of the heart. Coronary artery disease causes approximately 60% of congestive heart failure. Acute myocardial infarction (AMI) due to obstruction of a coronary artery is a common initiating event that can lead ultimately to heart failure. A myocardial ischemia may, for example, cause a portion of a myocardium of the heart to lose its ability to contract. Prolonged ischemia can lead to infarction of a portion of the myocardium (heart muscle) wherein the heart muscle dies and become scar tissue. Once this tissue dies, it no longer functions as a muscle and cannot contribute to the pumping action of the heart. When the heart tissue is no longer pumping effectively, that portion of the myocardium is said to be hypokinetic, meaning that it is less contractile than the uncompromised myocardial tissue. As this situation worsens, the local area of compromised myocardium may in fact bulge out as the heart contracts, further decreasing the hearts ability to move blood forward. When local wall motion moves in this way it is said to be dyskinetic. The dyskinetic portion of the myocardium may stretch and eventually form an aneurysmic bulge.
One problem with a large dilated left ventricle is that there is a significant increase in wall tension and/or stress both during diastolic filling and during systolic contraction. In a normal heart, the adaptation of muscle hypertrophy (thickening) and ventricular dilatation maintain a fairly constant wall tension for systolic contraction. However, in a failing heart, the ongoing dilatation is greater than the hypertrophy and the result is a rising wall tension requirement for systolic contraction. This is felt to be an ongoing insult to the muscle myocyte resulting in further muscle damage. In response, the heart tissue remodels to accommodate the chronically increased filling pressures, further increasing the work that the now-compromised myocardium must perform. This vicious cycle of cardiac failure results in the symptoms of congestive heart failure such as shortness of breath on exertion, edema in the periphery, nocturnal dypsnia (a characteristic shortness of breath that occurs at night after going to bed), weight gain, and fatigue, to name a few. The increase in wall stress also occurs during diastolic filling. The stress increase requires a larger amount of oxygen supply, which can result in exhaustion of the myocardium leading to a reduced cardiac output of the heart.
Prior treatments for heart failure associated with such dilatation fall into three general categories. The first being pharmacological treatment, for example, diuretics and ACE inhibitors. The second being assist devices, for example, pumps. Finally, surgical treatments also have been experimented with, for example, Dor or Jatene procedure, or left ventricular reconstruction (LVR).
A surgical procedure for reconstruction of the left ventricle, developed by Dr. Vincent Dor, involves surgery via sternotomy by placing the patient on a heart-lung machine. In this operation, the scar tissue is excluded, and a patch is placed where the scar was excluded in order to sculpt the contour of the restored ventricle, and thus, reshape the heart. This results in more efficient contractile function, as the ejection fraction increases and forward output improves. The technique requires open chest surgery (sternotomy or thoracotomy), and is universally considered an invasive procedure. Understandably, the risk, extended recovery period, and discomfort of the sternal incision act as a deterrent to patients and their physicians despite the need to address the disease state for which the procedure is designed.
Hence, it will be beneficial to achieve the desired sizing and shaping of the heart without the highly invasive open chest procedure. A minimally invasive procedure, for example one that is done using a catheter that is inserted into the femoral vein or artery and that accesses the left ventricle, could be highly desirable. Such a procedure shall be able to identify and exclude the infracted tissue, in a way that is comparable to the identification of the infracted tissue is accomplished by simple visualization in an open procedure, and maintain or create the apex that is necessary to recreate the proper functioning of a CHF heart. A proper recreation of the apex of the heart is essential for maintaining effective cardiac contraction.
As mentioned above, the infracted tissue is easily identified during an open chest surgery by visualization. During a closed chest procedure where the heart is accessed using minimally invasive techniques, as contemplated here, it is not possible to visually differentiate the infracted tissue from viable or reversibly-ischemic myocardium. While MRI and nuclear-uptake studies can identify the presence of scar, these are currently not feasible intraoperatively.
Thus, there is a need for sensing infarcted myocardium in the septum from the right or left ventricle, along with a method or device to reduce the left ventricular volume while preserving the apex, and, then to appropriately realign the apex of the left ventricle and alter the geometry and decrease the wall tension in order to improve cardiac ejection fraction).